After completing Outrider, you have unlocked Snail Trail. This challenge of GTA San Andreas game involves killing of an unknown journalist and his informer. Let us look at its walk through. To summarize:

First and foremost, arrange a bike as you have to chase a train.

Collect the sniper rifle hidden by Frank Tenpenny nearby. Location of the rifle will be marked on your game map with a green color blip.

Then chase the train whose position is shown on your map and it is nearby your garage. Inside it is a reporter whom you have to kill to complete Snail Trail mission.

It stops at a station and he gets out and prepares to meet a journalist.

Follow him on bike till both meet at a place and then kill both using sniper rifle to complete the challenge and to unlock Ice Cold Killa.

Be careful as the oncoming train may kill you

Note: While chasing the train, you should always be behind and not along side. If you are alongside then the oncoming trains on other track will kill you to fail the mission.

I will jolt down few other points. Carl Johnson gets no money for completing it as it is given by Tenpenny and his police team who are a bunch of corrupt officers. This challenge is easy to complete but it does take some time during the chase.

When you follow your target, a spook o meter appears on your gaming screen. If that meter becomes full then your target is alerted and you fail Snail Trail in GTA game.